1. Field of the Invention
The invention relates to a signal used in the transmission of data in a communication system, wherein the signal is comprised of continuous, successive cells. The invention further relates to a method for synchronizing a receiver relative to the cells of such a signal, a method for generating the above-named signal, and transmitting and receiving circuits used to implement this method.
2. Description of the Background
In packet-oriented data transmission, such as, for example, in an ATM system (ATM=asynchronous transfer mode), the receiver must recognize (in English, packet delineation) the start time of the incoming packets (also called cells). The quality of this synchronization significantly affects the overall performance of the system. A poor "packet delineation" increases proportionately the number of data packets that are lost, and can thereby, for example, destroy the performance of other processing steps.
Cell synchronization should--first of all--be as immune as possible to bit errors and bit patterns that may be present within the transmitted data (so-called mimics: random patterns that simulate a synchronization pattern) and will lead to synchronization error. Second, in the case of a synchronization error, the receiver should be capable of extricating itself from this situation independently. Third, and finally, it should be possible to implement the method at the lowest possible cost in terms of hardware. Generally, the cost in terms of hardware increases proportionally to reliability requirements. To this extent, then, the first two requirements stand in direct contrast to the third requirement.
In communication systems (especially in networks having several nodes), in addition to user data, monitoring and control data usually must also be transmitted. The monitoring data may be based upon the user data or to some given system conditions.
The system user is interested primarily in having his data transmitted at the highest possible speed. It would thus be to his benefit to have the largest possible band width at his disposal. For physical reasons, or due to standardized requirements, however, the overall band width that is available is limited. The transmission of control data can thus result in a necessary reduction in the band width available for user data. In order to leave the largest possible band width available to the user, the monitoring and/or control data should be transmitted as efficiently as possible.